1. Field of the Invention
The present invention relates to a knock control apparatus for an internal combustion engine.
2. Description of the Related Art
FIG. 1 shows an example of a structure of a general internal combustion engine and peripheral equipment. In the drawing, reference numeral 18 designates an internal combustion engine (hereinafter referred to as an engine) mounted in a vehicle, and this engine 18 is connected to an intake pipe 15 and an exhaust pipe 16. A downstream portion of the intake pipe 15 is constructed so as to branch to introduce intake air into respective cylinders of the engine 18, and the exhaust pipe 16 is constructed by branch portions corresponding to the respective cylinders and a collecting portion where the branch portions are collected. A throttle valve operated by a driver is provided at an upstream side of the intake pipe 15, and a throttle sensor 2 for outputting a signal proportional to an opening degree of the throttle valve is provided at a rotating shaft of the throttle valve. An ISC valve 17 is provided in a bypass parallel to the throttle valve, and an air cleaner 4, an intake air temperature sensor 3 for outputting a signal proportional to an intake air temperature, and an air flow sensor 1 for outputting a signal proportional to an intake air amount are provided at an upstream side of the throttle valve. At an intermediate portion of the intake pipe 15, as shown in the drawing, an EGR valve 8 is provided, and a bypass extending to the exhaust pipe 16 from the vicinity of the EGR valve 8 is provided. In the vicinity of the connection portion of the exhaust pipe 16 with the bypass, an O2 sensor 6 for outputting a signal proportional to a residual oxygen concentration in exhaust gas is provided.
An injector 10 for fuel injection is provided at each of the branch portions of the downstream portion of the intake pipe 15, and a predetermined amount of fuel sent through a delivery pipe 19 is injected into the engine 18 from the injector 10. The engine 18 is provided with a water temperature sensor 14 for outputting a signal proportional to the temperature of cooling water for cooling the engine 18 and a knock sensor 13 for detecting knock. Further, the engine 18 is provided with an ignition coil 9 corresponding to each cylinder, and a crank angle sensor 5 for outputting a signal proportional to the revolution speed of the engine 18. The signals of the respective sensors are inputted to an ECU 12 constituted of a microcomputer, and the ECU 12 carries out an operation for controlling the injector 10, the igniter and the like on the basis of the input signals, and outputs control signals.
An operation thereof will be described. When a driver turns a key and switches on an ignition at the time of start of the engine, current starts flowing through the ECU 12 for controlling the engine, and various sensors and actuators fixed to the engine 18 as well. Thereafter, when the driver turns a start switch (SW) 7, a stator is connected to a battery 11, thereby cranking the engine 18. When the engine 18 is cranked, the ECU 12 starts the fuel injection into the respective cylinders, and controls the engine 18 so that the respective cylinders are ignited.
FIG. 4 is a block diagram showing a structure of a conventional knock control apparatus for an internal combustion engine. FIG. 5 is an explanatory view showing a variation of each value in the conventional apparatus of FIG. 4. In FIG. 4, reference numerals 12 and 13 designate the ECU and the knock sensor shown in FIG. 1, respectively. The structure in the ECU 12 will be described. Reference numeral 20 designates a knock I/F circuit including a band pass filter 21 and a peak hold 22, in which an output signal from the knock sensor 13 is inputted, only a knock intrinsic frequency component is extracted from the output signal of the knock sensor by the band pass filter 21, and the output signal of the band pass filter in a predetermined period (B6xc2x0 to A104xc2x0) of each cylinder is peak-held by the peak hold portion 22. Reference numeral 24 designates an A/D conversion portion for A/D converting the peak hold signal outputted from the knock I/F circuit 20. Reference numeral 25 designates a BGL including an averaging portion 26 and a threshold (BGL) calculation portion 27, in which the A/D converted peak hold signal is averaged and amplified to obtain a threshold level (BGL) for a knock judgement. Reference numeral 28 designates a compare subtraction portion, which compares the peak hold signal with the BGL, judges the presence of occurrence of knock, and outputs a signal proportional to the intensity of knock. Reference numeral 29 designates an every one ignition delay angle amount calculation portion, which calculates a delay angle amount proportional to the intensity of knock for every one ignition from the knock judgement result of the compare subtraction portion 28. Reference numeral 30 designates a knock delay angle amount calculation portion, which integrates the delay angle amount for every one ignition and calculates a knock correction amount of ignition timing, however, in the case where knock does not occur, an advance angle return is made. Reference numeral 31 designates an A/D conversion portion for A/D converting a knock sensor output signal outputted from the knock sensor 13. Reference numeral 32 designates a knock sensor fail detection portion, which detects failure (disconnection, short circuit, etc.) of the knock sensor 13 on the basis of the A/D converted knock sensor output signal, and makes a predetermined amount delay angle correction.
An operation thereof will be described. A knock intrinsic frequency component is extracted from the output signal of the knock sensor 13 by the band pass filter 21 and is amplified. The signal after the processing is, as shown in FIG. 5, peak-held during a predetermined period (B6xc2x0 (BTDC6xc2x0 CA) to A104xc2x0 (ATDC104xc2x0 CA)) after ignition of each cylinder. The peak hold value is compared with a knock judgement level at that time, and a knock judgement is made. This knock judgement level is determined in such a manner that a prescribed averaging processing from the peak hold value is carried out, and the calculation from the averaged value (multiplying it by a coefficient and adding an offset thereof) is carried out. In this averaging processing, in view of the compatibility between stabilization of the knock judgement level (suppression of fluctuation due to the variation of knock sensor signal level for each cycle) and followingness to the change of an average signal level due to the change of an operating state, two-stage filter processing and a suitable filter averaging coefficient are set.
The conventional knock control apparatus is constructed as described above, and in general, in accordance with the change of the peak hold value (noise level), and the knock judgement level is also sequentially calculated to be updated to a level suitable for the operating state of the engine at that time (suitable for the knock judgement and causing no erroneous judgement). However, in the case where the noise level is rapidly changed (increased), there occurs a state where the calculation of the knock judgement level can not follow, there temporarily occurs a state where the knock judgement level is low with respect to the noise level, and there has been a problem in that a knock erroneous judgement due to noise can occur.
As examples of the knock erroneous judgement, for example, the following two examples can be enumerated.
(1) At the time of rapid change (increase) in a noise level by the rapid increase of engine revolution.
(2) In a GDI engine, at the time when the generation timing of mechanical noise at the time of injector operation is changed from a state where it is outside a knock control detection period of a knock sensor output signal to a state where it is within the detection period thereof by the switching of an operating mode (fuel injection timing).
The present invention has been made to solve such problems, and has an object to obtain a knock control apparatus for an internal combustion engine, which can prevent the occurrence of a knock erroneous judgement due to noise in a rapid change of a knock sensor output signal level (noise level) at a transition, while knock controllability is secured.
In view of the above object, a knock control apparatus for an internal combustion engine of the present invention, which makes a knock judgement by comparing a peak hold value of a knock sensor output signal with a knock judgement level calculated from the peak hold value, comprising: transition state judgement means for judging whether a transition state occurs, on the basis of a change of an operating state of an internal combustion engine and under a predetermined judgement condition; and correction value calculation means for calculating, in a case wherein it is judged that the transition state occurs, a correction value of the peak hold value of the knock sensor output signal at a time of judgement of the transition state and during a predetermined time after the judgement.
The transition state may be in an acceleration mode, and the transition state judgement means may judge whether the acceleration mode occurs, on the basis of a revolution variation of the internal combustion engine.
Alternatively, the transition state may be in an acceleration mode, and the transition state judgement means judges whether the acceleration mode occur, on the basis of a throttle variation.
Further, the transition state may be at an operating mode switching time.